<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
<meta name="viewport" content="width=device-width">
<meta name="theme-color" content="#222"><meta name="generator" content="Hexo 7.3.0">

  <link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon-next.png">
  <link rel="icon" type="image/png" sizes="32x32" href="/images/favicon-32x32.ico">
  <link rel="icon" type="image/png" sizes="16x16" href="/images/favicon-16x16.ico">
  <link rel="mask-icon" href="/images/logo.svg" color="#222">

<link rel="stylesheet" href="/css/main.css">



<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" integrity="sha256-wiz7ZSCn/btzhjKDQBms9Hx4sSeUYsDrTLg7roPstac=" crossorigin="anonymous">
  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/animate.css/3.1.1/animate.min.css" integrity="sha256-PR7ttpcvz8qrF57fur/yAx1qXMFJeJFiA6pSzWi0OIE=" crossorigin="anonymous">
  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/fancyapps-ui/5.0.28/fancybox/fancybox.css" integrity="sha256-6cQIC71/iBIYXFK+0RHAvwmjwWzkWd+r7v/BX3/vZDc=" crossorigin="anonymous">
  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/pace/1.2.4/themes/green/pace-theme-minimal.css">
  <script src="https://cdnjs.cloudflare.com/ajax/libs/pace/1.2.4/pace.min.js" integrity="sha256-gqd7YTjg/BtfqWSwsJOvndl0Bxc8gFImLEkXQT8+qj0=" crossorigin="anonymous"></script>

<script class="next-config" data-name="main" type="application/json">{"hostname":"sumumm.github.io","root":"/","images":"/images","scheme":"Gemini","darkmode":false,"version":"8.19.2","exturl":false,"sidebar":{"position":"left","display":"post","padding":18,"offset":12},"copycode":{"enable":true,"style":"mac"},"fold":{"enable":true,"height":300},"bookmark":{"enable":false,"color":"#222","save":"auto"},"mediumzoom":false,"lazyload":true,"pangu":false,"comments":{"style":"tabs","active":null,"storage":true,"lazyload":false,"nav":null},"stickytabs":false,"motion":{"enable":true,"async":true,"transition":{"menu_item":"fadeInDown","post_block":"fadeIn","post_header":"fadeInDown","post_body":"fadeInDown","coll_header":"fadeInLeft","sidebar":"fadeInUp"}},"i18n":{"placeholder":"搜索...","empty":"没有找到任何搜索结果：${query}","hits_time":"找到 ${hits} 个搜索结果（用时 ${time} 毫秒）","hits":"找到 ${hits} 个搜索结果"},"path":"/search.xml","localsearch":{"enable":true,"trigger":"auto","top_n_per_article":1,"unescape":false,"preload":false}}</script><script src="/js/config.js"></script>

    <meta name="description" content="本文主要是C语言基础——结构体、联合体占用空间计算的相关笔记，若笔记中有错误或者不合适的地方，欢迎批评指正😃。">
<meta property="og:type" content="article">
<meta property="og:title" content="LV01-18-C语言-结构体、联合体占用空间">
<meta property="og:url" content="https://sumumm.github.io/post/73f35e84.html">
<meta property="og:site_name" content="苏木">
<meta property="og:description" content="本文主要是C语言基础——结构体、联合体占用空间计算的相关笔记，若笔记中有错误或者不合适的地方，欢迎批评指正😃。">
<meta property="og:locale" content="zh_CN">
<meta property="og:image" content="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/1.gif">
<meta property="og:image" content="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220723194454122.png">
<meta property="og:image" content="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220723195127642.png">
<meta property="og:image" content="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220723204022488.png">
<meta property="og:image" content="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220724101808691.png">
<meta property="article:published_time" content="2022-07-22T02:58:29.000Z">
<meta property="article:modified_time" content="2025-06-13T16:25:56.986Z">
<meta property="article:author" content="苏木">
<meta property="article:tag" content="LV01-C语言基础">
<meta name="twitter:card" content="summary">
<meta name="twitter:image" content="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/1.gif">


<link rel="canonical" href="https://sumumm.github.io/post/73f35e84.html">



<script class="next-config" data-name="page" type="application/json">{"sidebar":"","isHome":false,"isPost":true,"lang":"zh-CN","comments":true,"permalink":"https://sumumm.github.io/post/73f35e84.html","path":"post/73f35e84.html","title":"LV01-18-C语言-结构体、联合体占用空间"}</script>

<script class="next-config" data-name="calendar" type="application/json">""</script>
<title>LV01-18-C语言-结构体、联合体占用空间 | 苏木</title>
  








    <script src="/js/browser_tools_disable.js"></script>

  <noscript>
    <link rel="stylesheet" href="/css/noscript.css">
  </noscript>
<!-- hexo injector head_end start --><link rel="stylesheet" href="https://unpkg.com/hexo-next-tags-plus@latest/lib/tag_plus.css" media="defer" onload="this.media='all'"><!-- hexo injector head_end end --></head>

<body itemscope itemtype="http://schema.org/WebPage" class="use-motion">
  <div class="headband"></div>

  <main class="main">
    <div class="column">
      <header class="header" itemscope itemtype="http://schema.org/WPHeader"><div class="site-brand-container">
  <div class="site-nav-toggle">
    <div class="toggle" aria-label="切换导航栏" role="button">
        <span class="toggle-line"></span>
        <span class="toggle-line"></span>
        <span class="toggle-line"></span>
    </div>
  </div>

  <div class="site-meta">

    <a href="/" class="brand" rel="start">
      <i class="logo-line"></i>
      <p class="site-title">苏木</p>
      <i class="logo-line"></i>
    </a>
      <p class="site-subtitle" itemprop="description">我的学习之路</p>
  </div>

  <div class="site-nav-right">
    <div class="toggle popup-trigger" aria-label="搜索" role="button">
        <i class="fa fa-search fa-fw fa-lg"></i>
    </div>
  </div>
</div>



<nav class="site-nav">
  <ul class="main-menu menu"><li class="menu-item menu-item-home"><a href="/" rel="section"><i class="fa fa-home fa-fw"></i>苏木的家</a></li><li class="menu-item menu-item-categories"><a href="/categories/" rel="section"><i class="fa fa-th fa-fw"></i>分类页<span class="badge">42</span></a></li><li class="menu-item menu-item-archives"><a href="/archives/" rel="section"><i class="fa fa-archive fa-fw"></i>归档页<span class="badge">673</span></a></li><li class="menu-item menu-item-flink"><a href="/flink/" rel="section"><i class="fa fa-link fa-fw"></i>友人帐</a></li><li class="menu-item menu-item-about"><a href="/about/" rel="section"><i class="fa fa-user fa-fw"></i>关于我</a></li>
      <li class="menu-item menu-item-search">
        <a role="button" class="popup-trigger"><i class="fa fa-search fa-fw"></i>搜索
        </a>
      </li>
  </ul>
</nav>



  <div class="search-pop-overlay">
    <div class="popup search-popup"><div class="search-header">
  <span class="search-icon">
    <i class="fa fa-search"></i>
  </span>
  <div class="search-input-container">
    <input autocomplete="off" autocapitalize="off" maxlength="80"
           placeholder="搜索..." spellcheck="false"
           type="search" class="search-input">
  </div>
  <span class="popup-btn-close" role="button">
    <i class="fa fa-times-circle"></i>
  </span>
</div>
<div class="search-result-container no-result">
  <div class="search-result-icon">
    <i class="fa fa-spinner fa-pulse fa-5x"></i>
  </div>
</div>

    </div>
  </div>

</header>
        
  
  <aside class="sidebar">

    <div class="sidebar-inner sidebar-nav-active sidebar-toc-active">
      <ul class="sidebar-nav">
        <li class="sidebar-nav-toc">
          文章目录
        </li>
        <li class="sidebar-nav-overview">
          站点概览
        </li>
      </ul>

      <div class="sidebar-panel-container">
        <!--noindex-->
        <div class="post-toc-wrap sidebar-panel">
            <div class="post-toc animated"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#%E4%B8%80%E3%80%81%E7%BB%93%E6%9E%84%E4%BD%93"><span class="nav-text">一、结构体</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#1-%E7%BB%93%E6%9E%84%E4%BD%93%E5%A4%A7%E5%B0%8F%E8%AE%A1%E7%AE%97%E8%A7%84%E5%88%99"><span class="nav-text">1.结构体大小计算规则</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-1%E6%88%90%E5%91%98%E7%9A%84%E6%95%B0%E6%8D%AE%E7%B1%BB%E5%9E%8B%E9%83%BD%E7%9B%B8%E5%90%8C"><span class="nav-text">1.1成员的数据类型都相同</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2%E6%88%90%E5%91%98%E7%9A%84%E6%95%B0%E6%8D%AE%E7%B1%BB%E5%9E%8B%E4%B8%8D%E7%9B%B8%E5%90%8C"><span class="nav-text">1.2成员的数据类型不相同</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-3%E7%89%B9%E6%AE%8A%E7%9A%84%E7%BB%93%E6%9E%84%E4%BD%93"><span class="nav-text">1.3特殊的结构体</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#2-%E5%AE%9E%E4%BE%8B%E5%88%86%E6%9E%90"><span class="nav-text">2.实例分析</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#2-1%E7%9B%B8%E5%90%8C%E6%88%90%E5%91%98%E7%BB%93%E6%9E%84%E4%BD%93"><span class="nav-text">2.1相同成员结构体</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-2%E7%89%B9%E6%AE%8A%E7%BB%93%E6%9E%84%E4%BD%93"><span class="nav-text">2.2特殊结构体</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-3%E6%88%90%E5%91%98%E4%B8%8D%E5%90%8C%E7%9A%84%E7%BB%93%E6%9E%84%E4%BD%93"><span class="nav-text">2.3成员不同的结构体</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-1%E5%AE%9E%E4%BE%8B1"><span class="nav-text">2.3.1实例1</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-2%E5%AE%9E%E4%BE%8B2"><span class="nav-text">2.3.2实例2</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-3%E5%AE%9E%E4%BE%8B3"><span class="nav-text">2.3.3实例3</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-4%E5%AE%9E%E4%BE%8B4"><span class="nav-text">2.3.4实例4</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-5%E5%AE%9E%E4%BE%8B5"><span class="nav-text">2.3.5实例5</span></a></li></ol></li></ol></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E4%BA%8C%E3%80%81%E8%81%94%E5%90%88%E4%BD%93"><span class="nav-text">二、联合体</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#1-%E8%81%94%E5%90%88%E4%BD%93%E5%A4%A7%E5%B0%8F%E8%AE%A1%E7%AE%97%E8%A7%84%E5%88%99"><span class="nav-text">1.联合体大小计算规则</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-1%E6%88%90%E5%91%98%E7%9A%84%E6%95%B0%E6%8D%AE%E7%B1%BB%E5%9E%8B%E9%83%BD%E7%9B%B8%E5%90%8C-1"><span class="nav-text">1.1成员的数据类型都相同</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-2%E6%88%90%E5%91%98%E7%9A%84%E6%95%B0%E6%8D%AE%E7%B1%BB%E5%9E%8B%E4%B8%8D%E7%9B%B8%E5%90%8C-1"><span class="nav-text">1.2成员的数据类型不相同</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#1-3%E7%89%B9%E6%AE%8A%E7%9A%84%E8%81%94%E5%90%88%E4%BD%93"><span class="nav-text">1.3特殊的联合体</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#2-%E5%AE%9E%E4%BE%8B%E5%88%86%E6%9E%90-1"><span class="nav-text">2.实例分析</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#2-1%E6%88%90%E5%91%98%E7%9B%B8%E5%90%8C%E7%9A%84%E8%81%94%E5%90%88%E4%BD%93"><span class="nav-text">2.1成员相同的联合体</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-2%E7%89%B9%E6%AE%8A%E8%81%94%E5%90%88%E4%BD%93"><span class="nav-text">2.2特殊联合体</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-3%E6%88%90%E5%91%98%E4%B8%8D%E5%90%8C%E7%9A%84%E8%81%94%E5%90%88%E4%BD%93"><span class="nav-text">2.3成员不同的联合体</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-1%E5%AE%9E%E4%BE%8B1-1"><span class="nav-text">2.3.1实例1</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#2-3-1%E5%AE%9E%E4%BE%8B2"><span class="nav-text">2.3.1实例2</span></a></li></ol></li></ol></li></ol></li></ol></div>
        </div>
        <!--/noindex-->

        <div class="site-overview-wrap sidebar-panel">
          <div class="site-author animated" itemprop="author" itemscope itemtype="http://schema.org/Person">
    <img class="site-author-image" itemprop="image" alt="苏木"
      src="/images/avatar.jpg">
  <p class="site-author-name" itemprop="name">苏木</p>
  <div class="site-description" itemprop="description">莫道桑榆晚，为霞尚满天</div>
</div>
<div class="site-state-wrap animated">
  <nav class="site-state">
      <div class="site-state-item site-state-posts">
        <a href="/archives/">
          <span class="site-state-item-count">673</span>
          <span class="site-state-item-name">日志</span>
        </a>
      </div>
      <div class="site-state-item site-state-categories">
          <a href="/categories/">
        <span class="site-state-item-count">42</span>
        <span class="site-state-item-name">分类</span></a>
      </div>
      <div class="site-state-item site-state-tags">
        <span class="site-state-item-count">43</span>
        <span class="site-state-item-name">标签</span>
      </div>
  </nav>
</div>
  <div class="links-of-author animated">
      <span class="links-of-author-item">
        <a href="https://github.com/sumumm" title="GitHub → https:&#x2F;&#x2F;github.com&#x2F;sumumm" rel="noopener me" target="_blank"><i class="fab fa-github fa-fw"></i>GitHub</a>
      </span>
  </div>

        </div>
      </div>
    </div>

    
  </aside>


    </div>

    <div class="main-inner post posts-expand">


  


<div class="post-block">
  
  

  <article itemscope itemtype="http://schema.org/Article" class="post-content" lang="zh-CN">
    <link itemprop="mainEntityOfPage" href="https://sumumm.github.io/post/73f35e84.html">

    <span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
      <meta itemprop="image" content="/images/avatar.jpg">
      <meta itemprop="name" content="苏木">
    </span>

    <span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
      <meta itemprop="name" content="苏木">
      <meta itemprop="description" content="莫道桑榆晚，为霞尚满天">
    </span>

    <span hidden itemprop="post" itemscope itemtype="http://schema.org/CreativeWork">
      <meta itemprop="name" content="LV01-18-C语言-结构体、联合体占用空间 | 苏木">
      <meta itemprop="description" content="">
    </span>
      <header class="post-header">
        <h1 class="post-title" itemprop="name headline">
          LV01-18-C语言-结构体、联合体占用空间
        </h1>

        <div class="post-meta-container">
          <div class="post-meta">
    <span class="post-meta-item">
      <span class="post-meta-item-icon">
        <i class="far fa-calendar"></i>
      </span>
      <span class="post-meta-item-text">发表于</span>

      <time title="创建时间：2022-07-22 10:58:29" itemprop="dateCreated datePublished" datetime="2022-07-22T10:58:29+08:00">2022-07-22</time>
    </span>
    <span class="post-meta-item">
      <span class="post-meta-item-icon">
        <i class="far fa-folder"></i>
      </span>
      <span class="post-meta-item-text">分类于</span>
        <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
          <a href="/categories/%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/" itemprop="url" rel="index"><span itemprop="name">嵌入式开发</span></a>
        </span>
          ，
        <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
          <a href="/categories/%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/" itemprop="url" rel="index"><span itemprop="name">01HQ课程体系</span></a>
        </span>
          ，
        <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
          <a href="/categories/%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/" itemprop="url" rel="index"><span itemprop="name">LV01-C语言基础</span></a>
        </span>
    </span>

  
    <span class="post-meta-break"></span>
    <span class="post-meta-item" title="本文字数">
      <span class="post-meta-item-icon">
        <i class="far fa-file-word"></i>
      </span>
      <span class="post-meta-item-text">本文字数：</span>
      <span>4.9k</span>
    </span>
    <span class="post-meta-item" title="阅读时长">
      <span class="post-meta-item-icon">
        <i class="far fa-clock"></i>
      </span>
      <span class="post-meta-item-text">阅读时长 &asymp;</span>
      <span>18 分钟</span>
    </span>
</div>

        </div>
      </header>

    
    
    
    <div class="post-body" itemprop="articleBody"><p>本文主要是C语言基础——结构体、联合体占用空间计算的相关笔记，若笔记中有错误或者不合适的地方，欢迎批评指正😃。</p>
<span id="more"></span>

<!-- Photo: https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/ -->

<details class="folding-tag" blue><summary> 点击查看使用工具及版本 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center" width=150px>Windows</td>        <td align="left">windows11</td>    </tr>    <tr>        <td align="center">Ubuntu</td>        <td align="left">Ubuntu16.04的64位版本</td>      </tr>    <tr>        <td align="center">VMware® Workstation 16 Pro</td>        <td align="left">16.2.3 build-19376536</td>      </tr>    <tr>        <td align="center">SecureCRT</td>        <td align="left">Version 8.7.2 (x64 build 2214)   -   正式版-2020年5月14日</td>      </tr>    <tr>        <td align="center">开发板</td>        <td align="left">正点原子 i.MX6ULL Linux阿尔法开发板</td>      </tr>    <tr>        <td align="center">uboot</td>        <td align="left">NXP官方提供的uboot，NXP提供的版本为uboot-imx-rel_imx_4.1.15_2.1.0_ga(使用的uboot版本为U-Boot 2016.03)</td>      </tr>    <tr>        <td align="center">linux内核</td>        <td align="left">linux-4.15(NXP官方提供)</td>      </tr>    <tr>        <td align="center">STM32开发板</td>        <td align="left">正点原子战舰V3(STM32F103ZET6)</td>      </tr></table>
              </div>
            </details>

<details class="folding-tag" blue><summary> 点击查看本文参考资料 </summary>
              <div class='content'>
              <table>    <tr><td align="center">参考方向  </td><td align="center">参考原文</td></tr>    <tr><td align="left">结构体大小的计算</td><td align="left"><a href="https://www.runoob.com/w3cnote/struct-size.html" target="_blank">结构体大小的计算 | 菜鸟教程 (runoob.com) <i class="fa fa-external-link-alt"></i> </a></td></tr>    <tr><td align="left">结构体大小计算</td><td align="left"><a href="https://blog.csdn.net/rongxy_/article/details/117260822" target="_blank">结构体大小计算_rongxy_的博客-CSDN博客_结构体数组字节大小计算 <i class="fa fa-external-link-alt"></i> </a></td></tr>    <tr><td align="left">关于结构体、联合体大小的计算</td><td align="left"><a href="https://blog.csdn.net/qq_29775205/article/details/86538154" target="_blank">关于结构体、联合体大小的计算_-子木的博客-CSDN博客_结构体和联合体大小 <i class="fa fa-external-link-alt"></i> </a></td></tr>    <tr><td align="left">内存对齐</td><td align="left"><a href="https://zhuanlan.zhihu.com/p/30007037" target="_blank">C/C++内存对齐详解 - 知乎 (zhihu.com) <i class="fa fa-external-link-alt"></i> </a></td></tr></table>
              </div>
            </details>

<details class="folding-tag" blue><summary> 点击查看相关文件下载 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center">---</td>        <td align="left">--- <a href="" target="_blank">  <i class="fa fa-external-link-alt"></i></a></td>      </tr></table>
              </div>
            </details>

<h1 id="一、结构体"><a href="#一、结构体" class="headerlink" title="一、结构体"></a><font size=3>一、结构体</font></h1><h2 id="1-结构体大小计算规则"><a href="#1-结构体大小计算规则" class="headerlink" title="1.结构体大小计算规则"></a><font size=3>1.结构体大小计算规则</font></h2><h3 id="1-1成员的数据类型都相同"><a href="#1-1成员的数据类型都相同" class="headerlink" title="1.1成员的数据类型都相同"></a><font size=3>1.1成员的数据类型都相同</font></h3><p>结构体占用空间&#x3D;成员个数×成员数据类型的长度。</p>
<h3 id="1-2成员的数据类型不相同"><a href="#1-2成员的数据类型不相同" class="headerlink" title="1.2成员的数据类型不相同"></a><font size=3>1.2成员的数据类型不相同</font></h3><p>类型不相同的时候，按结构体默认的字节对齐一般满足三个准则：</p>
<ul>
<li>（1）结构体变量的首地址能够被其最宽基本类型成员的大小所整除；</li>
<li>（2） 结构体每个成员相对于结构体首地址的偏移量（ offset ）都是成员大小的整数倍（ 0 被认为是任何数的整数倍），如有需要编译器会在成员之间加上填充字节（ internal adding ）；</li>
<li>（3）当没有定义  #pragma pack(value)  这种指定  value  字节进行对齐时，整体的大小在满足为最大数据类型所占字节的倍数下要达到所占内存最小（<strong>最大数据类型所占字节数的最小整数倍</strong>）。当定义了  #pragma pack(value) ，以  value 字节进行对齐时，它整体的大小必须为  value  的最小整数倍。如有需要编译器会在最末一个成员之后加上填充字节（ trailing padding ）。</li>
</ul>
<p><strong>【方法】</strong>后来发现，其实可以按照下边的方法来计算：</p>
<p>（1）首先找出成员变量中<strong>最大数据类型占用的字节数</strong> Lmax ；</p>
<p>（2）所有成员分析时都按照 Lmax 为准，先画一个含有 Lmax 个字节空位，然后各个成员按照大小开始往上填；</p>
<p>（3）成员相对于首地址偏移量需要是成员类型大小的整数倍，不是整数倍的可以在前边补空字节，若这个成员大小加上偏移量超过 Lmax ，则移到下一行（再画一个含有 Lmax 字节的空位）；</p>
<details class="folding-tag" blue><summary> 点击查看例子 </summary>
              <div class='content'>
              <figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">char</span> b;</span><br><span class="line">	<span class="type">int</span> c;</span><br><span class="line">	<span class="type">double</span> d;</span><br><span class="line">&#125; S1;</span><br></pre></td></tr></table></figure><img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/1.gif" alt="1" style="zoom:50%;" />
              </div>
            </details>

<h3 id="1-3特殊的结构体"><a href="#1-3特殊的结构体" class="headerlink" title="1.3特殊的结构体"></a><font size=3>1.3特殊的结构体</font></h3><p>对于一个没有任何成员的结构体，在 C 中占用空间为 0 ，而在 C++ 中它占用的空间为 1 字节，这是因为 struct 在 C++ 中相当于类。 </p>
<h2 id="2-实例分析"><a href="#2-实例分析" class="headerlink" title="2.实例分析"></a><font size=3>2.实例分析</font></h2><h3 id="2-1相同成员结构体"><a href="#2-1相同成员结构体" class="headerlink" title="2.1相同成员结构体"></a><font size=3>2.1相同成员结构体</font></h3><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">TEST1</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">int</span> a;</span><br><span class="line">	<span class="type">int</span> b;</span><br><span class="line">	<span class="type">int</span> c[<span class="number">2</span>]; </span><br><span class="line">&#125;;</span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">TEST2</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">char</span> b;</span><br><span class="line">	<span class="type">char</span> c[<span class="number">2</span>];</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="class"><span class="keyword">struct</span> <span class="title">TEST1</span> <span class="title">A</span>;</span></span><br><span class="line">	<span class="class"><span class="keyword">struct</span> <span class="title">TEST2</span> <span class="title">B</span>;</span></span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(A)=%ld,sizeof(A.a)=%ld,sizeof(A.b)=%ld,sizeof(A.c)=%ld\n&quot;</span>, <span class="keyword">sizeof</span>(A), <span class="keyword">sizeof</span>(A.a), <span class="keyword">sizeof</span>(A.b), <span class="keyword">sizeof</span>(A.c));</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;&amp;A     =%p\n&amp;A.a   =%p\n&amp;A.b   =%p\n&amp;A.c[0]=%p\n&amp;A.c[1]=%p\n&quot;</span>, &amp;A, &amp;A.a, &amp;A.b, &amp;A.c[<span class="number">0</span>], &amp;A.c[<span class="number">1</span>]);</span><br><span class="line">	</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(B)=%ld,sizeof(B.a)=%ld,sizeof(B.b)=%ld,sizeof(B.c)=%ld\n&quot;</span>, <span class="keyword">sizeof</span>(B), <span class="keyword">sizeof</span>(B.a), <span class="keyword">sizeof</span>(B.b), <span class="keyword">sizeof</span>(B.c));</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;&amp;B     =%p\n&amp;B.a   =%p\n&amp;B.b   =%p\n&amp;B.c[0]=%p\n&amp;B.c[1]=%p\n&quot;</span>, &amp;B, &amp;B.a, &amp;B.b, &amp;B.c[<span class="number">0</span>], &amp;B.c[<span class="number">1</span>]);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line">sizeof(A)=16,sizeof(A.a)=4,sizeof(A.b)=4,sizeof(A.c)=8</span><br><span class="line">&amp;A     =0x7ffe9c0871e0</span><br><span class="line">&amp;A.a   =0x7ffe9c0871e0</span><br><span class="line">&amp;A.b   =0x7ffe9c0871e4</span><br><span class="line">&amp;A.c[0]=0x7ffe9c0871e8</span><br><span class="line">&amp;A.c[1]=0x7ffe9c0871ec</span><br><span class="line">sizeof(B)=4,sizeof(B.a)=1,sizeof(B.b)=1,sizeof(B.c)=2</span><br><span class="line">&amp;B     =0x7ffe9c0871dc</span><br><span class="line">&amp;B.a   =0x7ffe9c0871dc</span><br><span class="line">&amp;B.b   =0x7ffe9c0871dd</span><br><span class="line">&amp;B.c[0]=0x7ffe9c0871de</span><br><span class="line">&amp;B.c[1]=0x7ffe9c0871df</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<h3 id="2-2特殊结构体"><a href="#2-2特殊结构体" class="headerlink" title="2.2特殊结构体"></a><font size=3>2.2特殊结构体</font></h3><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">TEST1</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="class"><span class="keyword">struct</span> <span class="title">TEST1</span> <span class="title">A</span>;</span></span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(A)=%ld\n&quot;</span>, <span class="keyword">sizeof</span>(A));</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;&amp;A=%p\n&quot;</span>, &amp;A);</span><br><span class="line"></span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">sizeof(A)=0</span><br><span class="line">&amp;A=0x7fff18b05457</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<h3 id="2-3成员不同的结构体"><a href="#2-3成员不同的结构体" class="headerlink" title="2.3成员不同的结构体"></a><font size=3>2.3成员不同的结构体</font></h3><h4 id="2-3-1实例1"><a href="#2-3-1实例1" class="headerlink" title="2.3.1实例1"></a><font size=3>2.3.1实例1</font></h4><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">short</span> b;</span><br><span class="line">	<span class="type">char</span> c;</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span>  a;</span><br><span class="line">	<span class="type">char</span>  b;</span><br><span class="line">	<span class="type">short</span> c;</span><br><span class="line">&#125; S2;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)=%ld,sizeof(S1.a)=%ld,sizeof(S1.b)=%ld,sizeof(S1.c)=%ld\n&quot;</span>,</span><br><span class="line">	        <span class="keyword">sizeof</span>(S1),    <span class="keyword">sizeof</span>(S1.a),    <span class="keyword">sizeof</span>(S1.b),    <span class="keyword">sizeof</span>(S1.c));</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;&amp;S1=%p \n&amp;S1.a=%p \n&amp;S1.b=%p \n&amp;S1.c=%p \n&quot;</span>,</span><br><span class="line">	        &amp;S1,     &amp;S1.a,     &amp;S1.b,     &amp;S1.c);</span><br><span class="line">	</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S2)=%ld,sizeof(S2.a)=%ld,sizeof(S2.b)=%ld,sizeof(S2.c)=%ld\n&quot;</span>,</span><br><span class="line">	        <span class="keyword">sizeof</span>(S2),    <span class="keyword">sizeof</span>(S2.a),    <span class="keyword">sizeof</span>(S2.b),    <span class="keyword">sizeof</span>(S2.c));</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;&amp;S2=%p \n&amp;S2.a=%p \n&amp;S2.b=%p \n&amp;S2.c=%p \n&quot;</span>,</span><br><span class="line">	        &amp;S2,     &amp;S2.a,     &amp;S2.b,     &amp;S2.c);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)=6,sizeof(S1.a)=1,sizeof(S1.b)=2,sizeof(S1.c)=1</span><br><span class="line">&amp;S1=0x5576e7e5b012 </span><br><span class="line">&amp;S1.a=0x5576e7e5b012 </span><br><span class="line">&amp;S1.b=0x5576e7e5b014 </span><br><span class="line">&amp;S1.c=0x5576e7e5b016 </span><br><span class="line">sizeof(S2)=4,sizeof(S2.a)=1,sizeof(S2.b)=1,sizeof(S2.c)=2</span><br><span class="line">&amp;S2=0x5576e7e5b018 </span><br><span class="line">&amp;S2.a=0x5576e7e5b018 </span><br><span class="line">&amp;S2.b=0x5576e7e5b019 </span><br><span class="line">&amp;S2.c=0x5576e7e5b01a </span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>我们来分析一下这两个结构体：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">short</span> b;</span><br><span class="line">	<span class="type">char</span> c;</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span>  a;</span><br><span class="line">	<span class="type">char</span>  b;</span><br><span class="line">	<span class="type">short</span> c;</span><br><span class="line">&#125; S2;</span><br></pre></td></tr></table></figure>

<ul>
<li>S1 结构体</li>
</ul>
<p>（1）成员 a ： char 类型，相对于首地址偏移量为 0 ，占据 1 字节空间；</p>
<p>（2）成员 b ： short 类型，此时前边有一个 char 类型，这就意味着该成员相对于首地址的偏移量为 1 ，而 short 类型占据 2 个字节，所以前边需要补一个字节，这就导致该成员的偏移量变为 2 ，然后再占据 2 个字节的空间；</p>
<p>（3）成员 c ： char 类型，相对于首地址的偏移量为 2+2&#x3D;4 ，是成员大小的整数倍，并占据 1 字节空间。</p>
<p>所以目前一共就是 2+2+1&#x3D;5 字节，但是，根据第三个原则，结构体的总大小需要是结构体成员中最大数据类型所占字节数的整数倍，也就是 2 的整数倍，所以需要在成员 c 后边补一个字节，这样整个结构体就占据了 6 个字节，即：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220723194454122.png" alt="image-20220723194454122" style="zoom:50%;" />

<ul>
<li>S2 结构体</li>
</ul>
<p>（1）成员 a ： char 类型，相对于首地址偏移量为 0 ，占据 1 字节空间；</p>
<p>（2）成员 b ： char 类型，此时前边有一个 char 类型，这就意味着该成员相对于首地址的偏移量为 1 ，而 char 类型占据 1 个字节，偏移量是成员大小的整数倍，不需要补字节；</p>
<p>（3）成员 c ： short 类型，相对于首地址的偏移量为 1+1&#x3D;2 ，是成员大小的整数倍，并占据 2 字节空间。</p>
<p>所以一共就是 1+1+2&#x3D;4 字节，即：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220723195127642.png" alt="image-20220723195127642" style="zoom:50%;" />

<h4 id="2-3-2实例2"><a href="#2-3-2实例2" class="headerlink" title="2.3.2实例2"></a><font size=3>2.3.2实例2</font></h4><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">char</span> b; </span><br><span class="line">	<span class="type">double</span> c;</span><br><span class="line">	<span class="type">short</span> d; </span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)=%ld,sizeof(S1.a)=%ld,sizeof(S1.b)=%ld,sizeof(S1.c)=%ld, sizeof(S1.d)=%ld\n&quot;</span>,</span><br><span class="line">	        <span class="keyword">sizeof</span>(S1),    <span class="keyword">sizeof</span>(S1.a),    <span class="keyword">sizeof</span>(S1.b),    <span class="keyword">sizeof</span>(S1.c),     <span class="keyword">sizeof</span>(S1.d));</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;&amp;S1=%p \n&amp;S1.a=%p \n&amp;S1.b=%p \n&amp;S1.c=%p \n&amp;S1.d=%p\n&quot;</span>,</span><br><span class="line">	        &amp;S1,     &amp;S1.a,     &amp;S1.b,     &amp;S1.c,     &amp;S1.d);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)=24,sizeof(S1.a)=1,sizeof(S1.b)=1,sizeof(S1.c)=8, sizeof(S1.d)=2</span><br><span class="line">&amp;S1=0x55da00a7c020 </span><br><span class="line">&amp;S1.a=0x55da00a7c020 </span><br><span class="line">&amp;S1.b=0x55da00a7c021 </span><br><span class="line">&amp;S1.c=0x55da00a7c028 </span><br><span class="line">&amp;S1.d=0x55da00a7c030</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>我们来分析一下这个结构体：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;   <span class="comment">/* # */</span> </span><br><span class="line">	<span class="type">char</span> b;   <span class="comment">/* # */</span> </span><br><span class="line">	<span class="type">double</span> c; <span class="comment">/* ######## */</span></span><br><span class="line">	<span class="type">short</span> d;  <span class="comment">/* ##000000 */</span></span><br><span class="line">&#125; S1;</span><br></pre></td></tr></table></figure>

<ul>
<li>S1 结构体</li>
</ul>
<p>（1）成员 a ： char 类型，相对于首地址偏移量为 0 ，占据 1 字节空间；</p>
<p>（2）成员 b ： char 类型，此时前边有一个 char 类型，这就意味着该成员相对于首地址的偏移量为 1 ，是成员大小的整数倍；</p>
<p>（3）成员 c ： double 类型，相对于首地址的偏移量为 1+1&#x3D;2 ，不是成员大小的整数倍，它的大小为 8 字节，所以前边补 6 个字节，那么这个成员的实际偏移量是 8 了，然后再占据 8 字节空间。</p>
<p>（4）成员 d ： short 类型，相对于首地址偏移量为 8+8&#x3D;16 ，是成员大小的整数倍。</p>
<p>所以目前一共就是 1+1+6+8+2&#x3D;18 字节，但是根据第三条规则，结构体的总大小需要是结构体成员中最大数据类型所占字节数的整数倍，也就是 8 的整数倍，所以最少需要在成员 d 后边补 6 个字节，这样整个结构体就占据了 24 个字节，即</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220723204022488.png" alt="image-20220723204022488" style="zoom:50%;" />

<h4 id="2-3-3实例3"><a href="#2-3-3实例3" class="headerlink" title="2.3.3实例3"></a><font size=3>2.3.3实例3</font></h4><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;   </span><br><span class="line">	<span class="type">int</span> b;   </span><br><span class="line">	<span class="type">char</span> c[<span class="number">5</span>];</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)=%ld,sizeof(S1.a)=%ld,sizeof(S1.b)=%ld,sizeof(S1.c)=%ld\n&quot;</span>,</span><br><span class="line">	        <span class="keyword">sizeof</span>(S1),    <span class="keyword">sizeof</span>(S1.a),    <span class="keyword">sizeof</span>(S1.b),    <span class="keyword">sizeof</span>(S1.c));</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)=16,sizeof(S1.a)=1,sizeof(S1.b)=4,sizeof(S1.c)=5</span><br><span class="line">&amp;S1=0x562315725020 </span><br><span class="line">&amp;S1.a=0x562315725020 </span><br><span class="line">&amp;S1.b=0x562315725024 </span><br><span class="line">&amp;S1.c=0x562315725028</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>我们来分析一下这个结构体：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;   </span><br><span class="line">	<span class="type">int</span> b;   </span><br><span class="line">	<span class="type">char</span> c[<span class="number">5</span>];</span><br><span class="line">&#125; S1;</span><br></pre></td></tr></table></figure>

<ul>
<li>S1 结构体</li>
</ul>
<p>（1）成员 a ： char 类型，相对于首地址偏移量为 0 ，占据 1 字节空间；</p>
<p>（2）成员 b ： int 类型，此时前边有一个 char 类型，这就意味着该成员相对于首地址的偏移量为 1 ，这就不是成员大小的整数倍了，前边补 3 个字节， b 的实际偏移量变成  4 然后再占据 4 字节空间；</p>
<p>（3）成员 c ： char 类型数组，包含 5 个成员，成员大小为 5 字节，相对于首地址的偏移量为 4+4&#x3D;8 ，偏移量是数据类型的整数倍。</p>
<p>所以目前一共就是 1+3+4+5&#x3D;13 字节，但是根据第三条规则，结构体的总大小需要是结构体成员中最大数据类型所占字节数的整数倍，也就是 4 的整数倍，所以最少需要在成员 c 后边补 3 个字节，这样整个结构体就占据了 16 个字节。</p>
<h4 id="2-3-4实例4"><a href="#2-3-4实例4" class="headerlink" title="2.3.4实例4"></a><font size=3>2.3.4实例4</font></h4><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">int</span> b;</span><br><span class="line">	<span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">	&#123;</span></span><br><span class="line">		<span class="type">char</span> c;</span><br><span class="line">		<span class="type">int</span> d;</span><br><span class="line">		<span class="type">double</span> e;</span><br><span class="line">	&#125; s;</span><br><span class="line">	<span class="type">float</span> f;</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)    =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1), &amp;S1);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.a)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.a), &amp;S1.a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.b)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.b), &amp;S1.b);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s), &amp;S1.s);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s.c)=%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s.c), &amp;S1.s.c);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s.d)=%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s.d), &amp;S1.s.d);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s.e)=%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s.e), &amp;S1.s.e);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.f)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.f), &amp;S1.f);</span><br><span class="line">	</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)    =32, addr=0x556695193040</span><br><span class="line">sizeof(S1.a)  = 1, addr=0x556695193040</span><br><span class="line">sizeof(S1.b)  = 4, addr=0x556695193044</span><br><span class="line">sizeof(S1.s)  =16, addr=0x556695193048</span><br><span class="line">sizeof(S1.s.c)= 1, addr=0x556695193048</span><br><span class="line">sizeof(S1.s.d)= 4, addr=0x55669519304c</span><br><span class="line">sizeof(S1.s.e)= 8, addr=0x556695193050</span><br><span class="line">sizeof(S1.f)  = 4, addr=0x556695193058</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>我们来分析一下这个结构体：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">int</span> b;</span><br><span class="line">	<span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">	&#123;</span></span><br><span class="line">		<span class="type">char</span> c;</span><br><span class="line">		<span class="type">int</span> d;</span><br><span class="line">		<span class="type">double</span> e;</span><br><span class="line">	&#125; s;</span><br><span class="line">	<span class="type">float</span> f;</span><br><span class="line">&#125; S1;</span><br></pre></td></tr></table></figure>

<ul>
<li>S1 结构体</li>
</ul>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/01HQ%E8%AF%BE%E7%A8%8B%E4%BD%93%E7%B3%BB/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/LV01-18-C%E8%AF%AD%E8%A8%80-%E7%BB%93%E6%9E%84%E4%BD%93%E3%80%81%E8%81%94%E5%90%88%E4%BD%93%E5%8D%A0%E7%94%A8%E7%A9%BA%E9%97%B4/img/image-20220724101808691.png" alt="image-20220724101808691" style="zoom:50%;" />

<h4 id="2-3-5实例5"><a href="#2-3-5实例5" class="headerlink" title="2.3.5实例5"></a><font size=3>2.3.5实例5</font></h4><p>该实例使用了 <strong>attribute</strong> 机制，设置了 <strong>packed</strong> 属性。</p>
<details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">struct</span> __<span class="title">attribute__</span>((__<span class="title">packed__</span>))</span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">int</span> b;</span><br><span class="line">	<span class="class"><span class="keyword">struct</span></span></span><br><span class="line"><span class="class">	&#123;</span></span><br><span class="line">		<span class="type">char</span> c;</span><br><span class="line">		<span class="type">int</span> d;</span><br><span class="line">		<span class="type">double</span> e;</span><br><span class="line">	&#125; s;</span><br><span class="line">	<span class="type">float</span> f;</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)    =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1), &amp;S1);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.a)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.a), &amp;S1.a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.b)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.b), &amp;S1.b);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s), &amp;S1.s);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s.c)=%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s.c), &amp;S1.s.c);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s.d)=%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s.d), &amp;S1.s.d);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.s.e)=%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.s.e), &amp;S1.s.e);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.f)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.f), &amp;S1.f);</span><br><span class="line">	</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)    =25, addr=0x556da3484020</span><br><span class="line">sizeof(S1.a)  = 1, addr=0x556da3484020</span><br><span class="line">sizeof(S1.b)  = 4, addr=0x556da3484021</span><br><span class="line">sizeof(S1.s)  =16, addr=0x556da3484025</span><br><span class="line">sizeof(S1.s.c)= 1, addr=0x556da3484025</span><br><span class="line">sizeof(S1.s.d)= 4, addr=0x556da3484029</span><br><span class="line">sizeof(S1.s.e)= 8, addr=0x556da348402d</span><br><span class="line">sizeof(S1.f)  = 4, addr=0x556da3484035</span><br></pre></td></tr></table></figure><p>这样的话，结构体的大小就直接是各个变量大小之和了。</p>
              </div>
            </details>

<h1 id="二、联合体"><a href="#二、联合体" class="headerlink" title="二、联合体"></a><font size=3>二、联合体</font></h1><h2 id="1-联合体大小计算规则"><a href="#1-联合体大小计算规则" class="headerlink" title="1.联合体大小计算规则"></a><font size=3>1.联合体大小计算规则</font></h2><h3 id="1-1成员的数据类型都相同-1"><a href="#1-1成员的数据类型都相同-1" class="headerlink" title="1.1成员的数据类型都相同"></a><font size=3>1.1成员的数据类型都相同</font></h3><p>联合体占用空间大小&#x3D;任一成员数据类型大小。</p>
<h3 id="1-2成员的数据类型不相同-1"><a href="#1-2成员的数据类型不相同-1" class="headerlink" title="1.2成员的数据类型不相同"></a><font size=3>1.2成员的数据类型不相同</font></h3><p>类型不相同的时候，分两种情况：</p>
<ul>
<li>没有定义  #pragma pack(value)</li>
</ul>
<p>联合体中最大成员所占内存的大小且必须为<strong>最大数据类型所占字节的最小倍数</strong>。</p>
<ul>
<li>定义了  #pragma pack(value)</li>
</ul>
<p>联合体中最大成员所占字节数必须为 value 的最小倍数。</p>
<h3 id="1-3特殊的联合体"><a href="#1-3特殊的联合体" class="headerlink" title="1.3特殊的联合体"></a><font size=3>1.3特殊的联合体</font></h3><p>对于一个没有任何成员的联合体，在 C 中占用空间为 0 。 </p>
<h2 id="2-实例分析-1"><a href="#2-实例分析-1" class="headerlink" title="2.实例分析"></a><font size=3>2.实例分析</font></h2><h3 id="2-1成员相同的联合体"><a href="#2-1成员相同的联合体" class="headerlink" title="2.1成员相同的联合体"></a><font size=3>2.1成员相同的联合体</font></h3><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">union</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">char</span> b;</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)    =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1), &amp;S1);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.a)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.a), &amp;S1.a);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)    = 1, addr=0x564129368011</span><br><span class="line">sizeof(S1.a)  = 1, addr=0x564129368011</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<h3 id="2-2特殊联合体"><a href="#2-2特殊联合体" class="headerlink" title="2.2特殊联合体"></a><font size=3>2.2特殊联合体</font></h3><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">union</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)    =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1), &amp;S1);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)    = 0, addr=0x564c0595f011</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<h3 id="2-3成员不同的联合体"><a href="#2-3成员不同的联合体" class="headerlink" title="2.3成员不同的联合体"></a><font size=3>2.3成员不同的联合体</font></h3><h4 id="2-3-1实例1-1"><a href="#2-3-1实例1-1" class="headerlink" title="2.3.1实例1"></a><font size=3>2.3.1实例1</font></h4><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">union</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">double</span> b;</span><br><span class="line">	<span class="type">char</span> c[<span class="number">9</span>];</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)    =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1), &amp;S1);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.a)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.a), &amp;S1.a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.b)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.b), &amp;S1.b);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.c)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.c), &amp;S1.c);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)    =16, addr=0x556b80767020</span><br><span class="line">sizeof(S1.a)  = 1, addr=0x556b80767020</span><br><span class="line">sizeof(S1.b)  = 8, addr=0x556b80767020</span><br><span class="line">sizeof(S1.c)  = 9, addr=0x556b80767020</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<h4 id="2-3-1实例2"><a href="#2-3-1实例2" class="headerlink" title="2.3.1实例2"></a><font size=3>2.3.1实例2</font></h4><p>该实例使用了 <strong>attribute</strong> 机制，设置了 <strong>packed</strong> 属性。</p>
<details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="class"><span class="keyword">union</span> __<span class="title">attribute__</span>((__<span class="title">packed__</span>))</span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line">	<span class="type">char</span> a;</span><br><span class="line">	<span class="type">double</span> b;</span><br><span class="line">	<span class="type">char</span> c[<span class="number">9</span>];</span><br><span class="line">&#125; S1;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1)    =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1), &amp;S1);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.a)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.a), &amp;S1.a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.b)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.b), &amp;S1.b);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sizeof(S1.c)  =%2ld, addr=%p\n&quot;</span>,<span class="keyword">sizeof</span>(S1.c), &amp;S1.c);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">sizeof(S1)    = 9, addr=0x5611cb03e018</span><br><span class="line">sizeof(S1.a)  = 1, addr=0x5611cb03e018</span><br><span class="line">sizeof(S1.b)  = 8, addr=0x5611cb03e018</span><br><span class="line">sizeof(S1.c)  = 9, addr=0x5611cb03e018</span><br></pre></td></tr></table></figure>
              </div>
            </details>


    </div>

    
    
    

    <footer class="post-footer">




    <div>
        
            <div style="text-align:center;color: #ccc;font-size:14px;">
            ----------本文结束
            <i class="fas fa-fan fa-spin" style="color: #FF1493; font-size: 1rem"></i>
            感谢您的阅读----------
            </div>
        
    </div>





  
  <div class="my_post_copyright"> 
    <p><span>文章标题:</span><a href="/post/73f35e84.html">LV01-18-C语言-结构体、联合体占用空间</a></p>
    <p><span>文章作者:</span><a href="/" title="欢迎访问 《苏木》 的学习笔记">苏木</a></p>
    <p><span>发布时间:</span>2022年07月22日 - 10:58</p>
    <p><span>最后更新:</span>2025年06月14日 - 00:25</p>
    <p><span>原始链接:</span><a href="/post/73f35e84.html" title="LV01-18-C语言-结构体、联合体占用空间">https://sumumm.github.io/post/73f35e84.html</a></p>
    <p><span>许可协议:</span><i class="fab fa-creative-commons"></i> <a rel="license" href= "https://creativecommons.org/licenses/by-nc-nd/4.0/" target="_blank" title="Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)">署名-非商业性使用-禁止演绎 4.0 国际</a> 转载请保留原文链接及作者。</p>  
  </div>
  


          <div class="post-tags">
              <a href="/tags/LV01-C%E8%AF%AD%E8%A8%80%E5%9F%BA%E7%A1%80/" rel="tag"><i class="fa fa-tag"></i> LV01-C语言基础</a>
          </div>

        

          <div class="post-nav">
            <div class="post-nav-item">
                <a href="/post/25ce70ee.html" rel="prev" title="通信协议-01-通信的基本概念">
                  <i class="fa fa-angle-left"></i> 通信协议-01-通信的基本概念
                </a>
            </div>
            <div class="post-nav-item">
                <a href="/post/51eca572.html" rel="next" title="LV01-17-C语言-attribute机制">
                  LV01-17-C语言-attribute机制 <i class="fa fa-angle-right"></i>
                </a>
            </div>
          </div>
    </footer>
  </article>
</div>






</div>
  </main>

  <footer class="footer">
    <div class="footer-inner">

  <div class="copyright">
    &copy; 2017 – 
    <span itemprop="copyrightYear">2025</span>
    <span class="with-love">
      <i class="fa fa-heart"></i>
    </span>
    <span class="author" itemprop="copyrightHolder">苏木</span>
  </div>
<div class="wordcount">
  <span class="post-meta-item">
    <span class="post-meta-item-icon">
      <i class="fa fa-chart-line"></i>
    </span>
      <span>站点总字数：</span>
    <span title="站点总字数">3.7m</span>
  </span>
  <span class="post-meta-item">
    <span class="post-meta-item-icon">
      <i class="fa fa-coffee"></i>
    </span>
      <span>站点阅读时长 &asymp;</span>
    <span title="站点阅读时长">225:26</span>
  </span>
</div>




    <span id="sitetime"></span>
    <script defer language=javascript>
        function siteTime()
        {
            window.setTimeout("siteTime()", 1000);
            var seconds = 1000;
            var minutes = seconds * 60;
            var hours = minutes * 60;
            var days = hours * 24;
            var years = days * 365;
            var today = new Date();
            var todayYear = today.getFullYear();
            var todayMonth = today.getMonth()+1;
            var todayDate = today.getDate();
            var todayHour = today.getHours();
            var todayMinute = today.getMinutes();
            var todaySecond = today.getSeconds();
            /*==================================================
            Date.UTC() -- 返回date对象距世界标准时间(UTC)1970年1月1日午夜之间的毫秒数(时间戳)
            year        - 作为date对象的年份，为4位年份值
            month       - 0-11之间的整数，做为date对象的月份
            day         - 1-31之间的整数，做为date对象的天数
            hours       - 0(午夜24点)-23之间的整数，做为date对象的小时数
            minutes     - 0-59之间的整数，做为date对象的分钟数
            seconds     - 0-59之间的整数，做为date对象的秒数
            microseconds - 0-999之间的整数，做为date对象的毫秒数
            ==================================================*/
            var t1 = Date.UTC(2017, 
                              5, 
                              19, 
                              0, 
                              0, 
                              0); //北京时间
            var t2 = Date.UTC(todayYear,todayMonth,todayDate,todayHour,todayMinute,todaySecond);
            var diff = t2-t1;
            var diffYears = Math.floor(diff/years);
            var diffDays = Math.floor((diff/days)-diffYears*365);
            var diffHours = Math.floor((diff-(diffYears*365+diffDays)*days)/hours);
            var diffMinutes = Math.floor((diff-(diffYears*365+diffDays)*days-diffHours*hours)/minutes);
            var diffSeconds = Math.floor((diff-(diffYears*365+diffDays)*days-diffHours*hours-diffMinutes*minutes)/seconds);
            document.getElementById("sitetime").innerHTML="已在这里 "+diffYears+" 年 "+diffDays+" 天 "+diffHours+" 小时 "+diffMinutes+" 分钟 "+diffSeconds+" 秒";
        }
        siteTime();
    </script>



    </div>
  </footer>

  
  <div class="back-to-top" role="button" aria-label="返回顶部">
    <i class="fa fa-arrow-up fa-lg"></i>
    <span>0%</span>
  </div>
  <div class="reading-progress-bar"></div>

<noscript>
  <div class="noscript-warning">Theme NexT works best with JavaScript enabled</div>
</noscript>


  
  <script src="https://cdnjs.cloudflare.com/ajax/libs/animejs/3.2.1/anime.min.js" integrity="sha256-XL2inqUJaslATFnHdJOi9GfQ60on8Wx1C2H8DYiN1xY=" crossorigin="anonymous"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/next-theme-pjax/0.6.0/pjax.min.js" integrity="sha256-vxLn1tSKWD4dqbMRyv940UYw4sXgMtYcK6reefzZrao=" crossorigin="anonymous"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/fancyapps-ui/5.0.28/fancybox/fancybox.umd.js" integrity="sha256-ytMJGN3toR+a84u7g7NuHm91VIR06Q41kMWDr2pq7Zo=" crossorigin="anonymous"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/lozad.js/1.16.0/lozad.min.js" integrity="sha256-mOFREFhqmHeQbXpK2lp4nA3qooVgACfh88fpJftLBbc=" crossorigin="anonymous"></script>
<script src="/js/comments.js"></script><script src="/js/utils.js"></script><script src="/js/motion.js"></script><script src="/js/next-boot.js"></script><script src="/js/pjax.js"></script>

  <script src="https://cdnjs.cloudflare.com/ajax/libs/hexo-generator-searchdb/1.4.1/search.js" integrity="sha256-1kfA5uHPf65M5cphT2dvymhkuyHPQp5A53EGZOnOLmc=" crossorigin="anonymous"></script>
<script src="/js/third-party/search/local-search.js"></script>




  <script src="/js/third-party/fancybox.js"></script>

  <script src="/js/third-party/pace.js"></script>


  




  

  <script class="next-config" data-name="enableMath" type="application/json">false</script><script class="next-config" data-name="mathjax" type="application/json">{"enable":true,"tags":"none","js":{"url":"https://cdnjs.cloudflare.com/ajax/libs/mathjax/3.2.2/es5/tex-mml-chtml.js","integrity":"sha256-MASABpB4tYktI2Oitl4t+78w/lyA+D7b/s9GEP0JOGI="}}</script>
<script src="/js/third-party/math/mathjax.js"></script>


 
        <div id="click-show-text"
            data-mobile = false
            data-text = 富强,民主,文明,和谐,自由,平等,公正,法制,爱国,敬业,诚信,友善
            data-fontsize = 15px
            data-random= false>
        </div>
       

      
        <script async src=https://cdn.jsdelivr.net/npm/hexo-next-mouse-effect@latest/click/showText.js></script>
      

      
    




    <script async src="/js/fancybox_param.js"></script>





<!-- APlayer本体 -->



</body>
</html>
